Estes Alpha III First and Second Flights - Each one unique; several questions.

[Purkeypilot]

Last night I build my Estes Alpha III. Wood glue and epoxy cured for about 18-20 hours and this evening I flew it for the first time. The rocket was build per the instructions and was not modified in any way. An Estes A8-3 engine was used for both flights. Both launches and flights were perfect with no problems. The Ejection charge successfully deployed the recovery system (12" Estes parachute) both times and the rocket was safely recovered both times. Though each recovery system deployment was a bit non standard. Here are the details and my concerns:

Flight 1 - 4 Sheets of Estes Recovery Wadding (3-4 recommended)

The ejection charge successfully deployed the recovery system, though I noticed that the decent rate was quite a bit higher than what it should have been, and it looked like the parachute did not quite fully open, so it was logical though I was not initially sure why, as it did not look tangled from about 300' or so. It was a grass landing and there was no damage as a result of the higher than normal descent rate. Upon closer post-flight inspection, I noticed that part of the parachute had been melted by the ejection charge gasses, and one of the parachute cords/strings, had actually passed through the melted section, and then during the decent, the plastic re-solidified around the cord/string making for a weird, hang up that caused the parachute to not be able to open fully.

In the end, I choked it up to me having messed up the wadding packing (though I did gently blow on the BT and did not feel anything of significance coming out of the engine mount). I managed to work the parachute enough to be more than usable on the second flight. I also changed up slightly the way I packed the Chute/Cords, and Shock Cord (because it was the tip of the parachute that was closest to the wadding/ejection charge that got melted). This time I "Z"ed the Shock Cord and placed it into the BT, then folded the shoot and lightly wrapped the parachute cords around it.

Flight 2 - 4 Sheets of Estes Recovery Wadding

The ejection charge was again successful in deploying the recovery system, and actually the descent and landing look great! After going and recovering the rocket from about 50 yards away, while walking back to the launch pad, I began inspecting everything, and noticed about 2 of the 4 squares of recovery wadding were remaining...okay, so maybe I packed it too much? I was thinking that if it did in fact get to packed, it was more than likely the result of how I packed the Shock Cord, which then in turn packed down the wadding when I inserted the Parachute assembly. Initially, I was not too concerned about it, as I have heard many instances of wadding/dog barf, remaining in the BT after the ejection charge.

Enter getting home and giving the Alpha III a good walk around - The first think I did was remove the remaining recovery wadding. It appeared to be about 2 sheets of the the original 4. The bottom half of the wad was completely black and singed (to be expected of course). Then I noticed that the Engine Hook was a bit loose, specifically, having excess play along the longitudinal axis. So, out came the 320 lumen Surefire, and I gave a look into the Engine Mount. I noticed that there appeared to be TWO tabs when the Engine Hook mounting tongue was. It turns out that the lower one that was blacked was actually a piece of the engine mount tube wall, that had somehow gotten "peeled" down. Then I started thinking about the fact that half the ejection wadding remained in the BT, and I began thinking that it could have caused excess pressure that forced the engine down against the engine hook, which in turn forced the engine hook down and slightly tore/peeled the wall of the engine mount tube.

There is 1/4" of movement with the engine hook (along the longitudinal axis). My concerns are:

After testing with a spend A8-3 engine case, the engine can be pushed in as far as the highest engine hook position will allow and can be pulled out as far as the lowest engine hook position will allow. This is 1/4" and I'm wondering it it will effect stability at all with a CG shift. Under thrust at launch and a 7-10 G acceleration, it will be forced higher, which in theory will keep the CG above the CP. During recovery system deployment, the pressure buildup in the BT will force the engine down, lowering the GC, though at that point, it does not really matter. What I AM concerned about is if the peeling/tearing of the engine mount tube will progress and worsen after each ejection charge and recovery system deployment???

I'm going to attempt to post several pictures for everyone to see, though my attempts to post pictures a couple days ago failed (I think it may be a result of my low post count).

Any advice or insight would be greatly appreciated. Thanks in advance to all!

 

[Screaminhelo]

It does sound like the wadding may have obstructed the charge. I can't offer any specific advice since this hasn't happened to me...yet. The nose cone could also be a bit tight, I have a feel that I go for but I have heard many suggest that the cone should stay in when the rocket is turned upside down but slip out with a gentle shake.

If I were in your shoes, I would consider cutting off the engine hook and just use a friction fit. The integrity of the engine hook mounting is now comprised and the play that you are seeing will get worse with every flight. For friction fit, I wrap a shot spiral of tape about the midpoint of the motor and 2 layers of 1/8" (or what ever overhang you desire) tape around the nozzle end for a thrust ring.

When I first read your post, I was skeptical of what I was reading. It seemed a bit incredible that enough pressure developed to do so much damage to the MMT with the gear still deploying but if my years as a mechanic have taught me anything I have, at least, learned that anything that slips the bonds of earth can fail in ways that you would never imagine.

 

[astrowolf67]

I agree, you should start using friction fit, because the repeated thrust and ejection will eventually tear the mount now that the hook is loose. Does the motor have play in the hook? Or is it the hook and motor both that have the 1/4 inch movement?

For pre flight packing, I like to push a sheet of wading in and sort of form a cup with it, then add a couple tube diameters worth of dog barf. Before I bundle the chute, I dust it with baby powder, then, after bundling, I use another sheet of wading wrapped around the chute to protect it from any burning particles that might get past the wadding/barf.

David

 

[hcmbanjo]

Regarding the torn engine mount tube - On your next build,
After the engine hook is in place, glue a square of card stock over the the top bend of the engine hook.
This will reinforce the thin engine mount tube.
I hate those tubes (the rough yellow ones) and will usually replace them with thicker ST-7 tubing.

On your Alpha,
Push the engine hook forward and slide in your engine.
Use 1/2" wide masking tape and wrap that around your engine and motor mount tube 1/2 width on each side.
You might want to coat the engine mount tube (if unpainted) with some medium CA glue
applied with a Q-tip. That will help prevent peeling of the engine mount tube when removing the tape after a flight.

Fred Shector had the best wadding advice -
Push the crumpled wadding into the top of the tube, put your mouth over the body tube.
Take a breath and blow in the tube from the top end. You'll feel the wadding hit the engine mount with a "thunk!"

If you use Quest wadding or flame resistant crepe paper, they are stiffer than the Estes treated toilet paper.
Take a square of the Quest or crepe paper and crush them into a small ball. This puts many folds into the sheet.
Open the square up and pack as usual.

One other thing I do - I don't get melted parachutes any more -



Wrap a small, last piece of wadding around the back end of your folded chute.
Don't use a full size sheet of wadding, cut it down to about three inches square.
You want this last piece of wadding to peel back and come off the chute at ejection.
Don't wrap it over the top.

https://modelrocketbuilding.blogspot.com/2014/11/wadding-wrap-tip.html

 

[Purkeypilot]

Thanks for the replies! I will plan on cutting the hook and using friction fit from now on. The nose cone was not super tight, but a shake would have likely not release it, so it sounds like it was a culmination of issues that led to the restriction. Now that I learned how to post pictures I will now. The mount moves up and down about 1/4" and as a result, the Engine can to.

 

[Purkeypilot]

Here are some pictures. I will attempt to get a few more in inside the Engine Mount Tube...

[/URL][/IMG]

[/URL][/IMG]

[/URL][/IMG]

[/URL][/IMG]

[/URL][/IMG]

[/URL][/IMG]

[/URL][/IMG]

 

[Screaminhelo]

That Alpha looks nice my friend!

I have started using friction fit in all of my builds. I fly LPR most of the time and I am just starting to get my MPR feet wet right now and it has worked well for me so far.

 

[Purkeypilot]

That Alpha looks nice my friend!

I have started using friction fit in all of my builds. I fly LPR most of the time and I am just starting to get my MPR feet wet right now and it has worked well for me so far.

Thanks! I put my all in building it and was really happy with how it turned out. That's just one reason why it sucks so bad that this happened after only TWO flights!

 

[Purkeypilot]

Quick question - I've been thinking a lot the last hour or two about converting my Alpha III to a Friction Fit Engine mounting system. I was thinking about the design of the existing Engine Mount and recalled that there was no Engine Block included in the design. Quite literally, the only thing preventing the engine from pushing all the way up into the BT, is the lug on the Engine Hook which goes through the wall of the MMT. It was this lug that was forced down, tearing the MMT, so there is 1/4" of play. If I convert it to a Friction Fit, should I attempt to completely remove the Engine Hook (how to do that, I'm not sure yet...) and install an Engine Block? Or is the friction from a masking tape wrap enough to prevent any longitudinal movement of the engine during thrust and ejection?

Thanks in advance!

 

[EXPjawa]

You'll need a block in there without the engine hook. Most kits now have you use both together - the end of the hook butts against the block. If you remove the bum hook, you'll need to have something to thrust against. I have had the same thing that you've run into here on older kits that don't include the block. And I've done the same thing - remove the hook and insert a block, then friction fit.

 

[Screaminhelo]

You could just cut the aft end of the hook off and check how far the existing tab allows you to insert your motor of choice and measure how much of the motor overhangs the aft end of the MMT. Let's say that the motor overhangs about 1/4", use 1/4" tape to wrap 2 to 3 layers of tape around the nozzle end of the motor to create a thrust ring. I have started building all of my motor mounts without a thrust ring or hook and use friction fit with a tape thrust ring on the motor instead. It does take a little more time to prep for launch but it is not that big of a deal to me.

 

[Purkeypilot]

You could just cut the aft end of the hook off and check how far the existing tab allows you to insert your motor of choice and measure how much of the motor overhangs the aft end of the MMT. Let's say that the motor overhangs about 1/4", use 1/4" tape to wrap 2 to 3 layers of tape around the nozzle end of the motor to create a thrust ring. I have started building all of my motor mounts without a thrust ring or hook and use friction fit with a tape thrust ring on the motor instead. It does take a little more time to prep for launch but it is not that big of a deal to me.

Oh ya, I see what you're saying. That's actually a pretty sharp idea! Thanks for the thought

 

[Screaminhelo]

Oh ya, I see what you're saying. That's actually a pretty sharp idea! Thanks for the thought

Somebody passed on to me, so I guess you could say that I am paying it forward.


Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[grapetang]

Hi Purkey,

Before you remove the hook, you may be able to salvage your torn MMT & still retain the hook. Since Estes gives you a slightly-longer-than-2.75" hook, you can use that extra room to anchor the existing hook.

• Note how much extra room/play you have left in the hook when you put a motor in.
• Get or make a 1/4" thrust ring/engine block (you can cut a 1/4" section off your expended motors).
• Cut a U-shaped notch at the forward end of the ring that's wide enough to fit past the hook inside the MMT (perhaps 1.5x-2x the hook width). Don't split the ring open into a split "C" ring; instead leave that noted extra hook length completely whole ("O") at the rear of the ring.
• Test it out: slide the ring into the MMT with the U notch facing the nose (lining it up with the hook) & the whole "O" ring section facing the rear; add an actual motor to see if everything fits in the hook. If it doesn't fit (motor + ring too long for the hook), make the U notch deeper to remove more length from the whole section & test again.
• When it does fit, remove the ring & motor and clean out the section above the forward hook end with a damp paper towel (if possible) to remove the soot.
• When clean & dry, put glue up near the forward end of the MMT, align the ring as before, and push it all the way in with an motor in one quick motion and remove the motor immediately afterwards. Use a glue that won't seize or lock up on you as you push.

If successful, the thrust ring/engine block will keep the motor from moving forward during thrust, and that short section of the ring anchors the hook & (hopefully) prevents backward movement when the ejection charge fires. To be safe, you can friction fit as well.

Hopefully that made sense. I can try illustrating if you need more details. Welcome to the hobby & to the forum! Good luck and happy flying!

 

[Purkeypilot]

Hi Purkey,

Before you remove the hook, you may be able to salvage your torn MMT & still retain the hook. Since Estes gives you a slightly-longer-than-2.75" hook, you can use that extra room to anchor the existing hook.

• Note how much extra room/play you have left in the hook when you put a motor in.
• Get or make a 1/4" thrust ring/engine block (you can cut a 1/4" section off your expended motors).
• Cut a U-shaped notch at the forward end of the ring that's wide enough to fit past the hook inside the MMT (perhaps 1.5x-2x the hook width). Don't split the ring open into a split "C" ring; instead leave that noted extra hook length completely whole ("O") at the rear of the ring.
• Test it out: slide the ring into the MMT with the U notch facing the nose (lining it up with the hook) & the whole "O" ring section facing the rear; add an actual motor to see if everything fits in the hook. If it doesn't fit (motor + ring too long for the hook), make the U notch deeper to remove more length from the whole section & test again.
• When it does fit, remove the ring & motor and clean out the section above the forward hook end with a damp paper towel (if possible) to remove the soot.
• When clean & dry, put glue up near the forward end of the MMT, align the ring as before, and push it all the way in with an motor in one quick motion and remove the motor immediately afterwards. Use a glue that won't seize or lock up on you as you push.

If successful, the thrust ring/engine block will keep the motor from moving forward during thrust, and that short section of the ring anchors the hook & (hopefully) prevents backward movement when the ejection charge fires. To be safe, you can friction fit as well.

Hopefully that made sense. I can try illustrating if you need more details. Welcome to the hobby & to the forum! Good luck and happy flying!

It makes perfect sense! I can imagine and visualize exactly what you are saying, and it's a genius idea! I'm going to do it for sure. You are quite good at explaining things it writing; well done! Thanks a million for the advice and assistance